In integrated circuit formation processes, semiconductor wafers are formed first, with semiconductor devices formed therein. The dies in the semiconductor wafers need to be packaged before they can be used. The dies may be bonded to other package components such as device dies, interposers, package substrates, printed circuit boards (PCBs) to form packages.
In addition, package-on-package (POP) structures may be formed. In a PoP structure, a top package, in which a device die is bonded, is bonded to a bottom package. The bottom package may also have a device die packaged therein. By adopting the PoP process, the integration level of the packages may be increased.
Since the materials in the package components have different coefficients of thermal expansion (CTEs), the package components may have a warpage during and after the packaging processes. The warpage may cause cold joints, and the failure of the packages.